Present techniques use a solid support which is usually a spherical polystyrene bead covered with a protein (e.g. a polypeptide coming from a vaccinated animal) which has anti-body type properties. In prior art apparatus, said support is disposed in a test tube type receptacle into which the compound containing the substance to be analysed is admitted and, after a suitable incubation period, the bead must be thoroughly washed with water to remove the excess compound. Said washing is manual as is the removal of the liquid, the tube being turned upside down and the open end of the tube having tabs which prevent the bead from falling out. The operation must then be repeated with the reagent, and its excess is again removed by washing, after which the tube is conveyed to an analysis unit proper e.g. for photocolorimetric analysis by injecting a suitable coloured reagent.
Although the principle of the support bead which successively holds the compound and the reagent is very simple and effective, the technique used gives little satisfaction: indeed, the washing operations carried out by hand are not very reliable because washes and temperature conditions differ on different occasions, and they are unsuitable for analyses using grouped tests with different dosages because of the numerous handling operations which are necessary.
That is why U.S. patent application No. 198,323 discloses a more reliable apparatus of simple design and perfectly suited to simultaneous analysis using general dosages and a minimum of handling.
This apparatus is constituted by an analysis rotor which has a plurality of peripheral cells each of which contains a reaction support together with means to convey washing liquid to each cell, each of said cells being provided with a peripheral liquid-removal orifice and having an upper portion provided with an inlet orifice for a compound and a reagent.
The means which allow the washing liquid to be conveyed are constituted in the main by a central inlet orifice from which radial pipes leave to connect said central orifice to each of the peripheral cells; preferably, the radial pipes are in a plane which is essentially perpendicular to the axis of rotation of the apparatus.
Such apparatus operates as follows:
The rotor is disposed beneath a feed device so as to inject a calibrated volume of compound such as serum, plasma or any other biological liquid which contains the substance to be analysed into each cell via an upper orifice, after this injection the compound is allowed to rest during the necessary incubation time.
The rotor is then set in motion and washing liquid is injected through the central orifice. At the outlet of the radial pipes, means are advantageously provided which form baffle plates so as to direct the liquid properly towards the bottom of the cell. For each cell, the effect of centrifuging is to expell via the peripheral orifice the excess compound which has not been fixed onto the solid support.
After washing, drying can optionally be performed by shutting off the washing liquid inlet while continuing centrifuging.
These operations are then repeated with a reagent which has the property of fixing itself onto the beginning of the chain built up during incubation.
After further incubation, removal of the loose excess, washing and drying a geiger counter is used to make a reading in the case where the reagent was marked with an isotope. If marking was done using an enzyme, a calibrated quantity of substrate is added to cause a coloured reaction which is directly read in the cell by a photometer.
The disadvantage of this apparatus, which is otherwise very advantageous, is that to fill each cell with compound and reagents, it is necessary to place the cell in communication with the feed devices concerned, e.g. pipettes which contain said compound and reagents. This limits the degree to which the rotor is self-contained in operation.
An aim of the invention is to provide an analysis apparatus of the above-described type in which the cells are fed with compound and reagent without using pipettes and using means which ensure a more self-contained mode of operation for the analysis apparatus.